The TARDIS that the man led them to - and it took seeing the TARDIS for Jack to actually connect he was another version of the Doctor, which given that he'd already seen the sonic screwdriver and heard him mention the TARDIS, was a pretty big indicator of how preoccupied he was with Brant's condition - wasn't the same one Jack knew, but similar enough that he didn't pay much attention to the differences. He just carried Brant in to the console room, mentally reached out to greet the TARDIS with a mildly obscene caress, and looked back at the Doctor. "Which way?"